Investment molding flask assembly

ABSTRACT

An investment molding flask assembly having a base with a central positioning boss protruded from a center thereof and at least one positioning annular groove defined therein around the central positioning boss, and a conical sleeve formed with a small opening end to be securely positioned on the base without any displacement in horizontal directions by means of the central positioning boss or the positioning annular groove. Whereby, the conical sleeve can be readily removable from a solidified semi-finished investment mold, and then the solidified semi-finished investment mold is sent into an oven independently for heating. Therefore the sleeve can be used repeatedly, and the investment mold can be manufactured rapidly and readily.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an improved molding flaskassembly used in investment casting, particularly to an investmentmolding flask assembly, which can be used repeatedly to manufactureinvestment molds rapidly and readily.

[0003] 2. Description of Related Art

[0004] Lost wax investment casting is used in the making of 3dimensioned articles such as a dental molds, metal ornaments, sculpturesetc. In a lost wax investment casting, a molding flask assembly isnormally used to form an investment mold, which is utilized to cooperatewith a spin casting apparatus to manufacture a desired article.

[0005] As shown in FIG. 8, a conventional investment molding flaskassembly comprises a base (50) having a spherical central positioningboss (51) protruded from a center thereof, and a cylindrical sleeve (60)having a lower opening end seated on a top of the base (50) andenclosing around the central positioning boss (51). A preliminary waxpattern (70) is securely fixed on a top end of the positioning boss (51)by means of melted wax drops (52). An investment material (80) ischarged into an internal space of the cylindrical sleeve (60) up to anupper opening end of the cylindrical sleeve (60) so as to completelyembed the wax pattern (70) in the cylindrical sleeve (60). After asemi-finished investment mold is solidified, the semi-finishedinvestment mold with the cylindrical sleeve (60) enclosed therearound issent into an oven to be heated together. Whereby the wax pattern (70) ismelted and dispersed from the investment mold with the desired moldingcavities defined therein. Casting material is then directed into themold cavity by means of centrifugal techniques utilizing the spincasting apparatus, and then the casting material hardens to form adesired article.

[0006] However, because the cylindrical sleeve (60) seated on the top ofthe base (50) is not retained at a fixed position, when the investmentmaterial is poured into the cylindrical sleeve (60), the cylindricalsleeve (60) may be moved sideways, and in this case the wax pattern (70)may not be embedded properly in the center of the investment mold.

[0007] The aforesaid conventional investment molding flask assemblystill has another important disadvantage. Because the sleeve (60) isformed as a cylindrical shape, it is not easy to remove the sleeve (60)from the semi-finished investment mold when the investment mold issolidified, and the cylindrical sleeve (60) enclosing the investmentmold has to be sent into the oven together with the investment mold.However, because the sleeve (60) and the investment material normallyhave different thermal expansion rates, after the investment mold andthe sleeve (60) are heated together, the sleeve (60) may be deformed oreven damaged by the overexpansion of the investment mold, or theinvestment mold may be deformed, therefore the sleeve (60) can not beused repeatedly, and the rate of finished product is low.

[0008] Therefore, it is an objective of the invention to provide animproved investment molding flask assembly to mitigate and/or obviatethe aforementioned problems.

SUMMARY OF THE INVENTION

[0009] A first object of the present invention is to provide an improvedinvestment molding flask assembly, which comprises a base having acentral positioning boss protruded from a center thereof and at leastone positioning annular groove defined therein around the centerthereof, and a conical sleeve having a small opening end thereof beingsecurely positioned on the base by means of the central positioning bossor a corresponding one of the at least one positioning annular grooveswithout any displacement in horizontal directions.

[0010] A second object of the present invention is to provide animproved investment molding flask assembly, wherein the sleeve isparticularly formed as a cone having a small opening end to bepositioned on the base and a large opening end, such that when asolidified semi-finished investment mold in the sleeve is inverted andplaced on a flat board, the sleeve is readily removable from thesolidified semi-finished investment mold. Thus, the sleeve can be usedrepeatedly.

[0011] Other objects, advantages and novel features of the inventionwill become more apparent from the following detailed description whentaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is an exploded perspective view of a first embodiment of aninvestment molding flask assembly in accordance with the invention;

[0013]FIG. 2 is a cross sectional view of the first embodiment of theinvestment molding flask assembly in accordance with the invention;

[0014]FIG. 3 is a cross sectional view of a second embodiment of theinvestment molding flask assembly in accordance with the invention;

[0015]FIG. 4 is a cross sectional view of a third embodiment of theinvestment molding flask assembly in accordance with the invention;

[0016]FIG. 5 is a cross sectional view of a fourth embodiment of theinvestment molding flask assembly in accordance with the invention;

[0017]FIG. 6 is a cross sectional view of a fifth embodiment of theinvestment molding flask assembly in accordance with the invention;

[0018]FIG. 7 is a cross sectional view of a sixth embodiment of theinvestment molding flask assembly in accordance with the invention; and

[0019]FIG. 8 is a cross sectional view of a conventional investmentmolding flask assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0020] As shown in FIG. 1, in a first embodiment of the presentinvention, an investment molding flask assembly comprises a base (10)and a sleeve (20) detachably positioned on a top surface of the base(10).

[0021] The base (10) is formed as a circular plate having a centralpositioning boss (11) protruded from a center thereof and twopositioning annular grooves (12) defined therein around the centerthereof. Wherein the central positioning boss (11) has a lower portionthereof formed as a cylinder and an upper portion thereof formed as acone. An upper end of the upper portion of the central positioning boss(11) is defined with a positioning recess (111) in a center thereof.

[0022] The sleeve (20) is formed as a hollow cone having a small openingend particularly dimensioned with an inner diameter slightly larger thanan outer diameter of the lower portion of the central positioning boss(11), and a large opening end with a diameter larger than that of thesmall opening end. The sleeve (20) is further defined with a maximumvolume mark (21) optionally labeled on an inner or outer surface nearthe large opening end thereof.

[0023] With reference to FIG. 2, a preliminary wax pattern (30) issecurely fixed on the upper end of the positioning boss (11) by means ofmelted wax (14) filled in the positioning recess (111). Then the smallopening end of the sleeve (20) is placed on the top surface of the base(10) and mounted around the central positioning boss (11). Because theinner diameter of the small end of the sleeve (20) is slightly largerthan the outer diameter of the lower portion of the central positioningboss (11), the small end of the sleeve (20) is retained at a fixedposition on the base (10) without any horizontal displacement. Next aninvestment material (40) is charged into an internal space of the sleeve(20) till its upper level is flush with the maximum volume mark (21) soas to embed the wax pattern (30) in the sleeve (20). After theinvestment material (40) is solidified, the whole investment moldtogether with the investment molding flask assembly can be invertedtogether and placed on a flat board. Because the sleeve (20) isspecially designed as a cone, the solidified semi-finished investmentmold is readily separated from the flat board by gravity and a smallimpact force acted upon a bottom of the base (10), whereby the sleeve(20) is rapidly removed from the semi-finished investment mold. Finallythe semi-finished investment mold is sent into an oven to be heatedtherein to obtain a finished investment mold.

[0024] In a second practicable embodiment as shown in FIG. 3, a sleeve(20 a) is formed as a two-stepped cone having a small opening endmounted around the central positioning boss (11), so that the sleeve (20a) is retained at a fixed position without any horizontal displacement.

[0025] In a third embodiment as shown in FIG. 4, a sleeve (20 b) isformed as a two-stepped cone having a small opening end thereof beingproperly inserted into an inner one of the annular groove (12), so thatthe sleeve (20 b) is retained at a fixed position without any horizontaldisplacement.

[0026] In a fourth embodiment as shown in FIG. 5, a sleeve (20 c) isformed as a cone having a small end thereof being properly inserted intothe inner one of the annular grooves (12), so that the sleeve (20 c) isretained at a fixed position without any displacement.

[0027] When a large article is to be molded in the investment moldingflask assembly, a large sleeve is necessary to permit a large waxpattern to be received in the center of the sleeve. As shown in FIG. 6,in a fifth embodiment a conical sleeve (20 d) having a small opening endthereof is properly inserted into an outer one of the annular grooves(12). A gasket ring (13) is further provided on the top surface of thebase (10) between the sleeve (20 d) and the central positioning boss(11) to prohibit the investment material (14) from going into the innerone of the two positioning annular rings (12). An inner edge of thegasket ring (13) is therearound formed with a flange having an upperconical surface extending flush with an outer surface of the cone-shapedupper portion of the central positioning boss (11). Whereby a pouringpit of the investment mold is formed with an upper opening larger thanthe outer diameter of the positioning boss so as to meet a volumerequirement of a large molding cavity formed in the investment mold.

[0028] A sixth embodiment as shown in FIG. 7 is basically same as thefifth embodiment except for a sleeve (20 e), which is formed as atwo-stepped cone.

[0029] The investment molding flask assembly of the invention has anadvantage that the sleeve is securely positioned on the base (10) bymeans of the positioning boss (11) or the positioning annular grooves(12), therefore it is retained in a fixed position without anyhorizontal displacement when the investment material (14) is chargedinto the internal space of the sleeve.

[0030] Another important advantage of the invention is that the sleevecan be used repeatedly and the investment mold can be made readily andrapidly, so that the production efficiency of the present invention ishigh and the production cost of the invention is low.

[0031] It is to be understood, however, that even though numerouscharacteristics and advantages of the present invention have been setforth in the foregoing description, together with details of thestructure and function of the invention, the disclosure is illustrativeonly, and changes may be made in detail, especially in matters of shape,size, and arrangement of parts within the principles of the invention tothe full extent indicated by the broad general meaning of the terms inwhich the appended claims are expressed.

What is claimed is:
 1. An investment molding flask assembly comprising:a base formed as a circular plate having a central positioning bossprotruded from a center of a top surface thereof, and at least onepositioning annular groove defined in the top surface around the centerthereof, wherein the central positioning boss is formed with acylindrical-shaped lower portion and a cone-shaped upper portion; asleeve formed as a cone having a small opening end thereof to besecurely positioned on the base without any horizontal displacement;whereby after a wax pattern is fixed on a top end of the centralpositioning boss, an investment material is charged into an internalspace of the sleeve to embed the wax pattern in the sleeve so as to forma solidified semi-finished investment mold, and then the solidifiedsemi-finished investment mold is allowed to be removed from the sleeveto be heated in an oven independently, therefore a finished investmentmold is rapidly obtained, and the investment molding flask assembly canbe used repeatedly.
 2. The investment molding flask assembly as claimedin claim 1, wherein the base is defined with two positioning annulargrooves in the top surface around the center thereof.
 3. The investmentmolding flask assembly as claimed in claim 1, wherein the sleeve has asmall opening end defined with a diameter slightly larger than an outerdiameter of the cylindrical-shaped lower portion of the centralpositioning boss.
 4. The investment molding flask assembly as claimed inclaim 1, wherein the sleeve has a small opening end defined with adiameter to be properly inserted into the at least one positioningannular groove.
 5. The investment molding flask assembly as claimed inclaim 1, wherein a positioning recess is defined in an upper end of thecone-shaped upper portion of the central positioning boss.
 6. Theinvestment molding flask assembly as claimed in claim 1, wherein thesleeve is formed as a cone.
 7. The investment molding flask assembly asclaimed in claim 1, wherein the sleeve is formed as a multi-steppedcone.
 8. The investment molding flask assembly as claimed in claim 1,wherein the sleeve is defined with a maximum volume mark at an innersurface near the large opening end thereof.
 9. The investment moldingflask assembly as claimed in claim 1, wherein the sleeve is defined witha maximum volume mark at an outer surface near the large opening endthereof.
 10. The investment molding flask assembly as claimed in claim1, wherein a gasket ring is provided on the top surface of the basebetween the sleeve and the central positioning boss, an inner edge ofthe gasket ring is formed therearound with a flange having an inner conesurface extending in flush with an outer surface of the cone-shapedupper portion of the central positioning boss.